Bone adapts to its mechanical and there is a growing consensus that osteocytes are mechanosensory cells involved in the regulation of both the bass and structure of bone. Two candidate mechanical signals are fluid flow and bone matrix strain. Although recent studies suggest that bone cells are more responsive to fluid flow, these cells respond biologically to mechanical strain as well. However, there is no correlation between the physical deformation of osteocytes resulting from these two disparate models of macroscopic stimulation. Furthermore, it is unknown how bone cells are deformed in-vivo resulting from in-vivo skeletal loading. The objective of the proposed research project is to understand how physical strain translates into osteocyte deformation. The major hypothesis to be tested in this proposal is that strains measured in-vivo are not an accurate measure of osteocyte deformation and that osteocyte mechanotransduction occurs at deformation levels substantially greater than strains measured in-vivo. This hypothesis has been formulated based on preliminary data that suggest strains near lacunae are magnified over macroscopic strains and that osteocyte deformation resulting from fluid flow in-vitro can be much greater than bone strains measured in-vivo. The major hypothesis will be tested by pursuing three specific aims: 1). Characterize the osteocyte lacunae deformations in cortical bone due to macroscopically applied specific strains. 2). Characterize the ex-vivo osteocyte deformation in mice bones subjected to whole bone loading. 3). Characterize the osteocyte deformations and resulting biological response due to mechanical stimulation of in-vitro cell cultures. The proposed research is innovative because it combines unique micromechanical analysis with biochemical and molecular biology techniques to gain a better understanding of osteocyte mechanotransduction. We expect our findings will help better define how osteocytes respond to mechanical stress and will help design more meaningful in-vitro experiments. This new knowledge will be significant because it will define osteocyte deformation within the bone matrix resulting from the application of macroscopic strain and will establish a correlation between this ex-vivo osteocyte deformation and cell deformations resulting from the two main methods of application of physical stimulus to in-vitro cell cultures and cell deformation in ex-vivo bone cultures. Furthermore, we will quantify osteocyte biological activity as a function of osteocyte deformation. In addition, this research activity should contribute to the general strategies for the prevention/treatment of bone diseases such as osteoporosis by helping to elucidate the underlying mechanisms of bone mechanotransduction. These findings may lead to pharmacological or gene therapy treatments targeted to prevent or mediate these diseases.